Disease was used as a weapon in 1767. I don't think they had the keeping and bearing of smallpox in mind, either.
They wanted a well-armed people to be a barrier to tyrants.
Armed with discriminating weapon, yes, I would agree.
Let us face it, many of the indiscriminate weapons I have mentioned would be a deadly risk to even possess. If you had VX nerve gas, could you transport it, transfer it among containers, and so on without killing yourself and all your neighbors? If you had smallpox, could you culture it and have it ready to employ without infecting yourself?
The risk of possession of these indiscriminate weapons well outwieghs their utility in use versus a criminal or a tyrannical government.
As far as a tyrannical government is concerned, I have long suspected that should this occur many army and airforce personnel will abandon their posts with very indiscriminate weaponry, and at that time a state of general war (civil war) would occur -- and at that time the Second Amendment would cease to have meaning, and instead reality would be the only limiting factor.
It's fine and good to limit such devices, but without an Amendment prohibiting WMD, biologicals etc I cannot agree. The founder's did not limit what weapons may be held by the citizens; they didn't limit weapons to only the army or militia; they didn't limit weapons to SELF-defense purposes only; they didn't limit the weapons held to be "discriminating" weapons only or otherwise create distinct classes; they didn't limit weapons to anyone by virtue of age, wealth or any other exclusionary tactic.
And should the last situation you described occur, the armies will be able to slaughter the civilian population regardless - not too many individuals could begin to have the necessary firepower to protect themselves. But the THREAT of having a small nuke might stop them and prevent that very situation from happening. A well-armed population is what kept the Japanese from invading the mainland in WWII. If they thought we all owned a P-51 Mustang maybe they wouldn't have attacked in the 1st place.